The botulinum neurotoxins, BoNTs, produced by Clostridium botulinum are among the most potent toxins known to man. The Centers for Disease Control and Prevention (CDC) has classified it as a potential bioweapon, Category A, because of its extreme potency and lethality, its ease of production and transport, and the need for prolonged intensive care among affected persons. This project participates on a collaboration focusing on the various serotypes and subtypes of the toxin with the overall goal of characterizing these variants at the DMA and protein level and developing a deeper understanding of neurotoxin action. We will focus on three major research areas: (1) continuing to deepen our understanding of the cell receptor recognition and binding processes as well as the translocation process by determining the structures of the toxin in complex with cell recognition receptor molecules, (2) developing a detailed understanding on how the recently developed antibodies (Abs), work and how we can then improve them, and (3) using structurebased approaches engineer the next generation broad spectrum diagnostic antibodies (working towards one antibody to recognize multiple toxin subtypes and serotypes). The study will characterize a number of BoNT variants to assess their impact on the development of diagnostics and therapeutics and to understand differences in biological action. In addition to the structures, the project will also produce highly purified protein samples that will be made available to its collaborators and other workers in the biodefense consortium.